Cleaning method, cleaning system, and method for manufacturing microstructure

ABSTRACT

According to one embodiment, a cleaning method is disclosed. The method can produce an oxidizing solution including an oxidizing substance by electrolyzing a dilute sulfuric acid solution. In addition, the method can supply a highly concentrated inorganic acid solution individually, sequentially, or substantially simultaneously with the oxidizing solution to a surface of an object to be cleaned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2009-220127, filed on Sep. 25,2009; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a cleaning method, acleaning system, and a method for manufacturing a microstructure.

BACKGROUND

Microstructures having fine wall bodies are manufactured on a surfaceusing lithography technology in fields such as semiconductor devices andMEMS (Micro Electro Mechanical Systems). Resists that are formed duringmanufacturing processes and then become unnecessary are peeled using anSPM (sulfuric acid hydrogen peroxide mixture) solution, i.e., a mixedliquid of concentrated sulfuric acid solution and aqueous hydrogenperoxide (for example, refer to JP-A 2007-123330 (Kokai)).

Here, it is necessary to repeatedly replenish the aqueous hydrogenperoxide because mixing the concentrated sulfuric acid solution and theaqueous hydrogen peroxide produces oxidizing substances (e.g.,peroxomonosulfuric acid) that react with water and decompose; and thedecomposed amounts must be replenished. Therefore, it is difficult tomaintain the solution mixing rate at a constant value. Moreover, theconcentration of the sulfuric acid decreases due to the increase of themixture amount of the aqueous hydrogen peroxide, and recyclingunfortunately can no longer be performed.

Therefore, technology has been proposed to peel the resist adhered to asilicon wafer and the like using oxidizing substances produced byelectrolyzing an aqueous solution of sulfuric acid (refer to JP-A2006-111943 (Kokai)). According to the technology discussed in JP-A2006-111943 (Kokai), the solution mixing rate can be stabilized byproducing the oxidizing substances from the aqueous solution of thesulfuric acid. However, the processing time unfortunately is longer thanthat of the case where the resist is peeled using an SPM solution. Also,even in the case where the resist is peeled using an SPM solution, theneed to increase productivity even more makes it necessary to shortenthe processing time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a cleaning system according to anembodiment;

FIGS. 2A and 2B are schematic views of the production mechanism of anoxidizing substance;

FIG. 3 is a graph of effects of the concentration of oxidizingsubstances and the concentration of inorganic acid on a peeling time;

FIG. 4 is a graph of temperature increase due to heat of reaction;

FIG. 5 is a graph of the relationship between a peeling time and thenumber of times being supplied sequentially;

FIG. 6 is a graph of effects of a processing temperature (a solutiontemperature);

FIG. 7 is a flowchart of a cleaning method;

FIG. 8 is a flowchart of a cleaning method according to anotherembodiment; and

FIG. 9 is a schematic view of a cleaning system according to anotherembodiment.

DETAILED DESCRIPTION

According to one embodiment, a cleaning method is disclosed. The methodcan produce an oxidizing solution including an oxidizing substance byelectrolyzing a dilute sulfuric acid solution. In addition, the methodcan supply a highly concentrated inorganic acid solution individually,sequentially, or substantially simultaneously with the oxidizingsolution to a surface of an object to be cleaned.

According to another embodiment, a cleaning system includes a sulfuricacid electrolysis unit, a dilute sulfuric acid supply unit, a cleaningprocessing unit, an inorganic acid supply unit, and an oxidizingsolution supply unit. The sulfuric acid electrolysis unit includes ananode, a cathode, a partitioning membrane provided between the anode andthe cathode, an anode chamber provided between the anode and thepartitioning membrane, and a cathode chamber provided between the anodeand the partitioning membrane. The sulfuric acid electrolysis unitproduces an oxidizing substance in the anode chamber by electrolyzing adilute sulfuric acid solution. The dilute sulfuric acid supply unitsupplies a dilute sulfuric acid solution to the anode chamber and thecathode chamber. The cleaning processing unit performs a cleaningprocessing of an object to be cleaned. The inorganic acid supply unitsupplies a highly concentrated inorganic acid solution to the cleaningprocessing unit. The oxidizing solution supply unit supplies anoxidizing solution including the oxidizing substance to the cleaningprocessing unit. The highly concentrated inorganic acid solution issupplied to the cleaning processing unit by the inorganic acid supplyunit individually, sequentially, or substantially simultaneously withthe oxidizing solution supplied by the oxidizing solution supply unit.

According to still another embodiment, a method is disclosed for forminga microstructure. The method can clean an object to be cleaned by thecleaning method described above and form a microstructure.

Embodiments will now be described with reference to the drawings.Similar components in the drawings are marked with like referencenumerals, and a detailed description is omitted as appropriate.

FIG. 1 is a schematic view illustrating a cleaning system according tothis embodiment.

As illustrated in FIG. 1, a cleaning system 5 includes a sulfuric acidelectrolysis unit 10, an inorganic acid supply unit 50, a cleaningprocessing unit 12, a solution circulation unit 14, and a dilutesulfuric acid supply unit 15.

The sulfuric acid electrolysis unit 10 has a function of electrolyzing asulfuric acid solution and producing an oxidizing substance in an anodechamber 30. Although the oxidizing capability of a solution includingoxidizing substances decreases when the solution including oxidizingsubstances is used to remove contaminants adhered to an object to becleaned, the sulfuric acid electrolysis unit 10 also has a function ofrecovering the reduced oxidizing capability.

The sulfuric acid electrolysis unit 10 includes an anode 32, a cathode42, a partitioning membrane 20 provided between the anode 32 and thecathode 42, the anode chamber 30 provided between the anode 32 and thepartitioning membrane 20, and a cathode chamber 40 provided between thecathode 42 and the partitioning membrane 20.

An upper end sealing unit 22 is provided at the upper end of thepartitioning membrane 20, the anode chamber 30, and the cathode chamber40; and a lower end sealing unit 23 is provided at the lower end of thepartitioning membrane 20, the anode chamber 30, and the cathode chamber40. The anode 32 opposes the cathode 42 with the partitioning membrane20 interposed therebetween. The anode 32 is supported by an anodesupport body 33; and the cathode 42 is supported by a cathode supportbody 43. A direct-current power source 26 is connected between the anode32 and the cathode 42.

The anode 32 is made of a conductive anode base member 34 and an anodeconductive film 35 formed on a surface of the anode base member 34. Theanode base member 34 is supported by the inner face of the anode supportbody 33; and the anode conductive film 35 faces the anode chamber 30.

The cathode 42 is made of a conductive cathode base member 44 and acathode conductive film 45 formed on a surface of the cathode basemember 44. The cathode base member 44 is supported by the inner face ofthe cathode support body 43; and the cathode conductive film 45 facesthe cathode chamber 40.

An anode inlet 19 is formed on the lower end side of the anode chamber30; and an anode outlet 17 is formed on the upper end side. The anodeinlet 19 and the anode outlet 17 communicate with the anode chamber 30.A cathode inlet 18 is formed on the lower end side of the cathodechamber 40; and a cathode outlet 16 is formed on the upper end side. Thecathode inlet 18 and the cathode outlet 16 communicate with the cathodechamber 40.

The inorganic acid supply unit 50 includes a tank 51 which retains ahighly concentrated inorganic acid solution, a pump 52, and an open/shutvalve 71. The tank 51, the pump 52, and the open/shut valve 71 areconnected to a dispense unit 61 via a piping line 53. The highlyconcentrated inorganic acid solution retained in the tank 51 can besupplied to the dispense unit 61 via the piping line 53 by the operationof the pump 52. In other words, the inorganic acid supply unit 50 has afunction of supplying the highly concentrated inorganic acid solutionretained in the tank 51 to the dispense unit 61 of the cleaningprocessing unit 12; and the highly concentrated inorganic acid solutionsupplied to the dispense unit 61 can be supplied to the surface of anobject W to be cleaned. It is favorable for the highly concentratedinorganic acid solution to be a solution having a dehydrating action.Examples of such include, for example, a concentrated sulfuric acidsolution having a sulfuric acid concentration not less than 90 weightpercent. Temperature control of the highly concentrated inorganic acidsolution can be performed by providing the tank 51 with a heater.

A highly concentrated inorganic acid solution also can be supplied tothe object W to be cleaned from a piping system separate from that ofthe solution including oxidizing substances (the oxidizing solution) byproviding a not-illustrated piping line and dispense unit separate froma piping line 74 and the dispense unit 61.

The cleaning processing unit 12 has a function of cleaning the object Wto be cleaned using the solution including oxidizing substances (theoxidizing solution) obtained in the sulfuric acid electrolysis unit 10and the highly concentrated inorganic acid solution supplied by theinorganic acid supply unit 50.

The oxidizing solution obtained in the sulfuric acid electrolysis unit10 is supplied to the dispense unit 61 provided in the cleaningprocessing unit 12 via the solution circulation unit 14. The highlyconcentrated inorganic acid solution is supplied by the inorganic acidsupply unit 50 to the dispense unit 61 provided in the cleaningprocessing unit 12. The oxidizing solution and the highly concentratedinorganic acid solution may be supplied sequentially; and the oxidizingsolution and the highly concentrated inorganic acid solution may besupplied substantially simultaneously.

The oxidizing solution and the highly concentrated inorganic acidsolution may be mixed; and the mixed liquid (the cleaning liquid) may besupplied. In the case where the highly concentrated inorganic acidsolution supplied by the inorganic acid supply unit 50 and the oxidizingsolution supplied by the sulfuric acid electrolysis unit 10 are suppliedsubstantially simultaneously to the piping line 74, the piping line 74forms a mixing unit mixing both solutions.

Also, a not-illustrated tank may be provided to mix the oxidizingsolution and the highly concentrated inorganic acid solution. In such acase, the not-illustrated tank is a mixing unit. By providing thenot-illustrated tank, the flow rate fluctuation of the mixed liquid (thecleaning liquid) can be buffered, the mixing rate can be adjusted, etc.Temperature control of the mixed liquid (the cleaning liquid) can beperformed by providing the not-illustrated tank and the piping line 74with a heater.

The dispense unit 61 has a dispensing nozzle for dispensing theoxidizing solution, the highly concentrated inorganic acid solution, andthe mixed liquid (the cleaning liquid) of the oxidizing solution and thehighly concentrated inorganic acid solution onto the object W to becleaned. A rotating table 62 is provided on which the object W to becleaned is placed to oppose the dispensing nozzle. The rotating table 62is provided in the interior of a cover 29. By dispensing the oxidizingsolution, the highly concentrated inorganic acid solution, and the mixedliquid (the cleaning liquid) of the oxidizing solution and the highlyconcentrated inorganic acid solution from the dispense unit 61 towardthe object W to be cleaned, the contaminants and unnecessary substances(e.g., the resist, etc.) can be removed from the top of the object W tobe cleaned in a short length of time. The removing of the contaminantsand unnecessary substances (e.g., the resist, etc.) in a short length oftime from the top of the object W to be cleaned is described below.

Although so-called single wafer processing is used in the cleaningprocessing unit 12 illustrated in FIG. 1, batch processing also may beused.

The oxidizing solution produced in the sulfuric acid electrolysis unit10 is supplied from the anode outlet 17 to the cleaning processing unit12 via the solution circulation unit 14. As a solution maintaining unit,the anode outlet 17 is connected to a tank 28 via a piping line 73 inwhich an open/shut valve 73 a is provided. The tank 28 is connected tothe dispense unit 61 via the piping line 74. The oxidizing solutionretained in the tank 28 is supplied to the dispense unit 61 via thepiping line 74 by the operation of a pump 81. An open/shut valve 74 a isprovided in the piping line 74 on the dispensing side of the pump 81. Inthis embodiment, the tank 28, the pump 81, etc., form an oxidizingsolution supply unit that supplies the oxidizing solution includingoxidizing substances to the cleaning processing unit 12. In such a case,the flow rate fluctuation of the oxidizing solution produced in thesulfuric acid electrolysis unit 10 can be buffered by retaining andmaintaining the oxidizing solution in the tank 28. Temperature controlof the oxidizing solution can be performed by providing the tank 28 witha heater.

The oxidizing solution discharged from the cleaning processing unit 12is recoverable by the solution circulation unit 14 and resuppliable tothe cleaning processing unit 12. For example, the oxidizing solutiondischarged from the cleaning processing unit 12 is suppliable to theanode inlet 19 of the sulfuric acid electrolysis unit 10 by passingthrough a returning tank 63, a filter 64, a pump 82, and an open/shutvalve 76 in this order. In other words, the oxidizing solution can becirculated between the sulfuric acid electrolysis unit 10 and thecleaning processing unit 12. In such a case, as necessary, the oxidizingsolution used during the cleaning processing can be supplied to thesulfuric acid electrolysis unit 10; subsequently, the oxidizing solutionincluding oxidizing substances obtained by performing electrolysis inthe sulfuric acid electrolysis unit 10 can be passed through the tank28, etc.; and the oxidizing solution can be supplied to the cleaningprocessing unit 12.

Here, as necessary, the oxidizing solution can be produced by supplyingdiluted sulfuric acid from the dilute sulfuric acid supply unit 15 tothe sulfuric acid electrolysis unit 10 as well as supplying the usedoxidizing solution to the sulfuric acid electrolysis unit 10, and thenperforming electrolysis. The oxidizing solution obtained here can bepassed through the tank 28, etc., and supplied to the cleaningprocessing unit 12. By repeating such re-utilization of the oxidizingsolution as much as possible, it is possible to reduce the amount of thematerials (chemical solutions, etc.) necessary to produce the oxidizingsolution and the amount of the waste fluid during the cleaningprocessing of the object W to be cleaned.

Alternatively, the oxidizing solution discharged from the cleaningprocessing unit 12 is suppliable to the tank 28 by passing through thereturning tank 63, the filter 64, the pump 82, and an open/shut valve 91in this order, that is, without passing through the sulfuric acidelectrolysis unit 10. Here, continuing, cleaning processing of theobject W to be cleaned can be performed by supplying the oxidizingsolution from the tank 28 to the cleaning processing unit 12. In such acase, the used oxidizing solution can be re-utilized during the cleaningprocessing. By repeating such re-utilization of the oxidizing solutionas much as possible, it is possible to reduce the amount of thematerials (chemical solutions, etc.) necessary to produce the oxidizingsolution and the amount of the waste fluid.

Similarly, the highly concentrated inorganic acid solution and the mixedliquid (the cleaning liquid) of the oxidizing solution and the highlyconcentrated inorganic acid solution discharged from the cleaningprocessing unit 12 can be circulated and re-utilized. In particular, inthe case where the inorganic acid is sulfuric acid, the amount of thedilute sulfuric acid supplied by the dilute sulfuric acid supply unit 15(a tank 60) can be reduced because the inorganic acid is a sourcematerial liquid of the oxidizing solution. In the case where problemsoccur when re-utilizing a mixture of the inorganic acid solution and theoxidizing solution, a not-illustrated returning tank, open/shut valve,etc., can be connected to the cleaning processing unit 12 for theinorganic acid solution to separate and recover the inorganic acidsolution and the oxidizing solution. In such a case, by supplying theinorganic acid solution and the oxidizing solution sequentially, theseparation and recovery can be performed during each supplying thereof.Separate re-utilization is possible by separate reprocessing, etc.

The returning tank 63 is provided with a discharge piping line 75 and adischarge valve 75 a having a function of discharging the contaminantsand unnecessary substances (e.g., the resist, etc.) cleaned and removedin the cleaning processing unit 12 to the outside of the system. Thefilter 64 has a function of filtering the contaminants and unnecessarysubstances (e.g., the resist, etc.) included in the oxidizing solution,the inorganic acid solution, and the mixed liquid (the cleaning liquid)discharged from the cleaning processing unit 12.

The dilute sulfuric acid supply unit 15 has a function of supplying adilute sulfuric acid solution to the sulfuric acid electrolysis unit 10(the anode chamber 30 and the cathode chamber 40). The dilute sulfuricacid supply unit 15 includes a pump 80 which supplies the dilutesulfuric acid solution to the anode chamber 30 and the cathode chamber40, the tank 60 which retains the dilute sulfuric acid, and open/shutvalves 70 and 72.

A dilute sulfuric acid solution having a sulfuric acid concentration notless than 30 weight percent and not more than 70 weight percent isretained in the tank 60. The pump 80 is driven such that the dilutesulfuric acid solution in the tank 60 passes through the open/shut valve70 and is supplied to the anode chamber 30 via the piping line on thedownstream side of the open/shut valve 76 and the anode inlet 19. Also,the pump 80 is driven such that the dilute sulfuric acid solution in thetank 60 passes through the open/shut valve 72 and is supplied to thecathode chamber 40 via a piping line 86 on the downstream side of theopen/shut valve 72 and the cathode inlet 18.

In this embodiment, damage of the partitioning membrane 20 due to theelectrolysis of the sulfuric acid can be suppressed because the sulfuricacid concentration of the solution supplied to the cathode side is low.In other words, water on the cathode side moves to the anode side duringthe electrolysis reaction of the sulfuric acid; the sulfuric acidconcentration of the solution on the cathode side increases; and thepartitioning membrane 20 easily deteriorates. Moreover, in the casewhere an ion exchange membrane is used as the partitioning membrane 20,the resistance of the ion exchange membrane increases as the watercontent decreases in the concentrated sulfuric acid solution; and thecontainer voltage undesirably increases. Therefore, to mitigate suchproblems as well, the resistance increase can be suppressed by supplyingdilute sulfuric acid to the cathode side to supply water to the ionexchange membrane.

By reducing the concentration of the sulfuric acid supplied to thesulfuric acid electrolysis unit 10, the production efficiency of theoxidizing substance (e.g., peroxomonosulfuric acid and peroxodisulfuricacid) included in the oxidizing solution can be increased. Increasingthe production efficiency of the oxidizing substance is described below.

The open/shut valves 70, 71, 72, 73 a, 74 a, 75 a, 76, and 91 describedabove also have a function of controlling the flow rate of the varioussolutions. The pumps 80, 81, and 82 also have a function of controllingthe flow velocities of the various solutions.

From the aspect of chemical resistance, the material of the anodesupport body 33, the cathode support body 43, the cathode outlet 16, theanode outlet 17, the cathode inlet 18, the anode inlet 19, and the cover29 of the cleaning processing unit 12, may favorably include, forexample, a fluorocarbon resin such as polytetrafluoroethylene.

The piping that supplies the oxidizing solution, the highly concentratedinorganic acid solution, and the mixed liquid (the cleaning liquid) ofthe oxidizing solution and the highly concentrated inorganic acidsolution to the cleaning processing unit 12 may include a fluorocarbonresin tube wound with insulation, etc. Such piping also may be providedwith in-line heaters made of fluorocarbon resin. The pumps that pump theoxidizing solution, the highly concentrated inorganic acid solution, andthe mixed liquid (the cleaning liquid) of the oxidizing solution and thehighly concentrated inorganic acid solution may include a bellows pumpmade of fluorocarbon resin having heat resistance and chemicalresistance.

The material of the tanks that retain the sulfuric acid solution mayinclude, for example, quartz. Each of the tanks may include an overflowcontrol device, temperature control device, etc., as appropriate.

The partitioning membrane 20 may include, for example, a neutral film(albeit having undergone hydrophilizing processing) including a PTFEporous partitioning membrane such as that having the product namePoreflon, etc., and a positive ion exchange membrane such as thosehaving the product names Nafion, Aciplex, Flemion, etc. The dimensionsof the partitioning membrane 20 are, for example, about 50 squarecentimeters. It is suitable for the upper end sealing unit 22 and thelower end sealing unit 23 to include, for example, an O ring coated withfluorocarbon resin.

The material of the anode conductive base member 34 may include, forexample, p-type silicon and valve metal such as niobium. Herein, “valvemetal” refers to a metal having the metal surface thereof uniformlycovered with an oxide film by anode oxidation and having excellentcorrosion resistance. The cathode conductive base member 44 may include,for example, n-type silicon.

The material of the anode conductive film 35 and the cathode conductivefilm 45 may include, for example, glassy carbon. From the aspect ofdurability, it is suitable to use a conductive diamond film in the casewhere a solution having a relatively high sulfuric acid concentration issupplied.

For both the anode and the cathode, the conductive film and the basemember may be formed of the same material. For example, in the casewhere glassy carbon is used as the cathode base member and in the casewhere a conductive diamond self-supporting film is used as the anodebase member, the base member itself forms a conductive film havingelectrocatalytic properties which can contribute to the electrolyzingreaction.

Although diamond has stable chemical, mechanical, and thermalproperties, it has been difficult to use diamond in an electrochemicalsystem because of poor conductivity. However, a conductive diamond filmcan be obtained by forming while supplying boron gas and nitrogen gasusing hot filament chemical vapor deposition (HF-CVD). The conductivediamond film has a wide “potential window” of, for example, 3 to 5 voltsand an electrical resistance of, for example, 5 to 100milli-ohm-centimeters.

Herein, the “potential window” is the minimum potential (not less than1.2 volts) necessary for the electrolysis of water. The “potentialwindow” differs by material quality. In the case where a material havinga wide “potential window” is used and electrolysis is performed at apotential in the “potential window,” an electrolyzing reaction having anoxidation-reduction potential inside the “potential window” may progresspreferentially to the electrolysis of water; and there are cases wherethe oxidation reaction or reduction reaction of a substance which doesnot easily undergo electrolysis can progress preferentially.Accordingly, decomposing and synthesizing is possible by using such aconductive diamond for substances which cannot undergo conventionalelectrochemical reactions.

In HF-CVD, decomposition is performed by supplying the source-materialgas to the tungsten filament in a high-temperature state. The radicalsnecessary for forming the film are formed. Subsequently, the radicalsdiffused into the substrate surface react with other reactive gases toform the film on the desired substrate.

The production mechanism of the oxidizing substance in the sulfuric acidelectrolysis unit 10 will now be described.

FIGS. 2A and 2B are schematic views illustrating the productionmechanism of the oxidizing substance. FIG. 2A is a schematic sidecross-sectional view of the sulfuric acid electrolysis unit. FIG. 2B isa schematic view illustrating the cross section along line A-A of FIG.2A.

As illustrated in FIGS. 2A and 2B, the anode 32 and the cathode 42 areprovided to oppose each other with the partitioning membrane 20interposed therebetween. The anode 32 is supported by the anode supportbody 33 with the anode conductive film 35 of the anode 32 facing theanode chamber 30. The cathode 42 is supported by the cathode supportbody 43 with the cathode conductive film 45 of the cathode 42 facing thecathode chamber 40. Electrolysis unit housings 24 are provided on bothend portions of each of the partitioning membrane 20, the anode supportbody 33, and the cathode support body 43.

A sulfuric acid solution (a dilute sulfuric acid solution) of 70 weightpercent, for example, is supplied from the tank 60 to the anode chamber30 via the anode inlet 19. The 70 weight percent sulfuric acid solution(the dilute sulfuric acid solution), for example, is supplied from thetank 60 also to the cathode chamber 40 via the cathode inlet 18.

By applying a positive voltage to the anode 32 and a negative voltage tothe cathode 42, an electrolysis reaction occurs in each of the anodechamber 30 and the cathode chamber 40. The reactions of chemical formula1, chemical formula 2, and chemical formula 3 occur in the anode chamber30.

2HSO₄ ⁻→S₂O₈ ²⁻+2H⁺+2e ⁻  Chemical formula 1

HSO₄ ⁻+H₂O→HSO₅ ⁻+2H⁺+2e ⁻  Chemical formula 2

2H₂O→4H⁺+4e ⁻+O₂↑  Chemical formula 3

Here, the water (H₂O) in chemical formula 2 and chemical formula 3 isthe water included as 30 percent of the 70 weight percent sulfuric acidsolution. In the anode chamber 30, the reaction of chemical formula 2produces peroxomonosulfuric acid ions (HSO₅ ⁻). The overall reaction ofchemical formula 4 occurs by the elementary reactions of chemicalformula 1 and chemical formula 3 to also produce peroxomonosulfuric acidions (HSO₅ ⁻) and sulfuric acid. Peroxomonosulfuric acid has a cleaningcapability higher than that of sulfuric acid.

S₂O₈ ²⁻+H⁺+H₂O→HSO₅ ⁻+H₂SO₄  Chemical formula 4

Alternatively, in some cases, the peroxomonosulfuric acid ions (HSO₅ ⁻)of chemical formula 4 are produced after hydrogen peroxide (H₂O₂) isproduced as illustrated by chemical formula 5 from the elementaryreactions of chemical formula 1 and chemical formula 3. In some cases,peroxodisulfuric acid (H₂S₂O₈) is produced by the reaction of chemicalformula 1. Chemical formula 4 and chemical formula 5 are second orderreactions from chemical formula 1.

S₂O₈ ²⁻+H⁺+H₂O→H₂O₂+H₂SO₄  Chemical formula 5

Hydrogen gas is produced in the cathode chamber 40 as illustrated bychemical formula 6. This occurs because hydrogen ions (H⁺) produced atthe anode move to the cathode via the partitioning membrane 20 and anelectrolysis reaction occurs. The hydrogen gas is discharged from thecathode chamber 40 via the cathode outlet 16.

2H⁺+2e ⁻→H₂↑  Chemical formula 6

In this embodiment as illustrated by chemical formula 7, oxidizingsubstances such as, for example, peroxomonosulfuric acid (H₂SO₅),peroxodisulfuric acid (H₂S₂O₈), etc., can be obtained by electrolyzingthe sulfuric acid solution; and an oxidizing solution including theseoxidizing substances can be obtained. Although hydrogen gas is producedas a by-product, the hydrogen gas does not affect the peeling of theresist, etc.

H₂SO₄+H₂O→oxidizing substances+H₂  Chemical formula 7

In the case where peroxomonosulfuric acid is used, the reaction ratewith organic substances such as the resist is high. Therefore, even theresist peeling, in which the amount to be removed is relatively large,can be completed in a short length of time. Also, in the case whereperoxomonosulfuric acid is used, peeling is possible at a lowtemperature. Therefore, the fine-tuning time for temperature ramp-up andthe like is unnecessary. Moreover, peroxomonosulfuric acid can beproduced stably in large amounts. Therefore, the reaction rate with theobject of removal can be increased even at low temperatures.

Here, to increase the production efficiency by shortening the processingtime, it is sufficient to increase the amount of the oxidizingsubstance. In such a case, the amount of oxidizing substances producedcan be increased by increasing the apparatus size, increasing theapplied power, increasing the amount of the dilute sulfuric acidsolution, etc. However, such actions lead to higher production costs andenvironmental impacts. Therefore, it is necessary to efficiently producethe oxidizing substance by increasing the electrolysis efficiency.

According to knowledge obtained by the inventors, in the case ofconstant electrolysis parameters (e.g., the amount of electricity, flowrate, temperature, etc.), more oxidizing substances can be produced byreducing the sulfuric acid concentration during the electrolyzing.Therefore, the production efficiency of the oxidizing substances (e.g.,peroxomonosulfuric acid and peroxodisulfuric acid) included in theoxidizing solution can be increased by reducing the sulfuric acidconcentration supplied to the sulfuric acid electrolysis unit 10.

However, according to other knowledge obtained by the inventors, theprocessing time for peeling and removing an organic substance such as aresist lengthens as the concentration of the inorganic acid such assulfuric acid decreases.

FIG. 3 is a graph illustrating the effects of the concentration of theoxidizing substances and the concentration of the inorganic acid on thepeeling time. The oxidizing substance concentration is plotted on thehorizontal axis. The peeling time is plotted on the vertical axis. InFIG. 3, B1 is the case where the sulfuric acid concentration is 70weight percent; B2 is the case where the sulfuric acid concentration is80 weight percent; B3 is the case where the sulfuric acid concentrationis 85 weight percent; B4 is the case where the sulfuric acidconcentration is 90 weight percent; and B5 is the case where thesulfuric acid concentration is 95 weight percent.

FIG. 3 shows that as the sulfuric acid concentration decreases, moreoxidizing substances are produced; and the concentration of theoxidizing substances therefore increases. Also, for the same sulfuricacid concentration, the peeling time shortens as the concentration ofthe oxidizing substances increases (as the amount of the oxidizingsubstances increases).

However, when comparing different sulfuric acid concentrations, thepeeling time shortens as the sulfuric acid concentration increases.

In other words, while more oxidizing substances can be produced as thesulfuric acid concentration decreases during the production stage of theoxidizing substances, the peeling time can be shortened by increasingthe sulfuric acid concentration during the peeling stage even while theamount of the oxidizing substances is the same.

Therefore, in this embodiment, a dilute sulfuric acid solution having asulfuric acid concentration not less than 30 weight percent and not morethan 70 weight percent is supplied to the sulfuric acid electrolysisunit 10. The highly concentrated inorganic acid solution (e.g., aconcentrated sulfuric acid solution having a sulfuric acid concentrationnot less than 90 weight percent) is supplied to the surface of theobject W to be cleaned without passing through the sulfuric acidelectrolysis unit 10.

Therefore, more oxidizing substances can be produced by increasing theelectrolysis efficiency of the sulfuric acid electrolysis unit 10. Also,the highly concentrated inorganic acid can be supplied to the surface ofthe object W to be cleaned without affecting the electrolysis efficiencyof the sulfuric acid electrolysis unit 10. As a result, a solutionhaving a high concentration of an inorganic acid such as sulfuric acidand including a large amount of oxidizing substances can be supplied tothe surface of the object W to be cleaned. Therefore, the processingtime can be shortened drastically.

Here, according to experiments performed by the inventors, the peelingtime of a resist was about 120 seconds when a dilute sulfuric acidsolution having a sulfuric acid concentration of 70 weight percent wassupplied to the sulfuric acid electrolysis unit 10, an oxidizingsolution was produced, and peeling of the resist was performed bysupplying the oxidizing solution to the surface of the object W to becleaned. On the other hand, the peeling time was shortened drasticallyto about 20 seconds when the dilute sulfuric acid solution having asulfuric acid concentration of 70 weight percent was supplied to thesulfuric acid electrolysis unit 10, the oxidizing solution was produced,and a concentrated sulfuric acid solution having a sulfuric acidconcentration of 98 weight percent was added to the oxidizing solutionto supply an oxidizing solution having a sulfuric acid concentration of82 weight percent to the surface of the object W to be cleaned.

While a high-speed operation semiconductor device is manufactured byimplanting an impurity with a high dose, an altered layer is formed inthe surface of the resist by the implanting of the impurity with thehigh dose. The resist having such an altered layer does not peel easily;and the desired peeling margin unfortunately cannot be obtained.

According to this embodiment, a highly concentrated inorganic acid andan oxidizing solution including a large amount of oxidizing substancescan be supplied to the surface of the object W to be cleaned. Therefore,the peelability of a resist can be increased even in the case where analtered layer is formed in the resist.

The heat of reaction can be utilized when a highly concentratedinorganic acid solution is mixed with an oxidizing solution which alsois a low-concentration inorganic acid solution. As the temperatureincreases, the reactivity of the oxidizing substances included in theoxidizing solution can be increased. Therefore, the processing time canbe shortened.

However, increasing the solution temperature of the sulfuric acidelectrolysis unit 10 and the inorganic acid supply unit 50 may causeproblems regarding the allowable temperature and strength of thecomponents (e.g., the piping lines, open/shut valves, pumps, and tanksof each unit, the cleaning processing unit cover, etc.). The componentsoften are formed of, for example, fluorocarbon resin, etc., to increasethe chemical resistance of the portions in contact with the highlyconcentrated inorganic acid solution and the oxidizing solution. In sucha case, the necessary strength may not be possible in the case where thetemperature is too high.

According to this embodiment, a heat of reaction can be generated bymixing the highly concentrated inorganic acid solution and the oxidizingsolution, which also is a low-concentration inorganic acid solution,prior to supplying to the object W to be cleaned or on the object W tobe cleaned. Therefore, the temperature increase of the components can besuppressed; and the reactivity of the oxidizing substance can beincreased by increasing the temperature of the mixed liquid.

FIG. 4 is a graph illustrating the temperature increase due to the heatof reaction. The temperature of the mixed liquid is plotted on thevertical axis. The concentration of the mixed liquid is plotted on thehorizontal axis. The temperature of each of the highly concentratedinorganic acid solution and the low-concentration inorganic acidsolution (the solution illustrated in FIG. 4 is of a concentratedsulfuric acid solution and a dilute sulfuric acid solution) prior to themixing is 88° C. C1 of FIG. 4 illustrates the case where a dilutesulfuric acid solution having a sulfuric acid concentration of 30 weightpercent is mixed with a concentrated sulfuric acid solution having asulfuric acid concentration of 98 weight percent. C2 of FIG. 4illustrates the case where a dilute sulfuric acid solution having asulfuric acid concentration of 50 weight percent is mixed with aconcentrated sulfuric acid solution having a sulfuric acid concentrationof 98 weight percent. C3 of FIG. 4 illustrates the case where a dilutesulfuric acid solution having a sulfuric acid concentration of 70 weightpercent is mixed with a concentrated sulfuric acid solution having asulfuric acid concentration of 98 weight percent.

FIG. 4 shows that a heat of reaction can be generated by mixinginorganic acids (sulfuric acids) of different concentrations; and theheat of reaction can be utilized to increase the temperature of themixed liquid. As the difference is increased between the concentrationsof the liquids to be mixed, or as the mixing ratio is set to dilute themixed liquid (as the mixing ratio is set to reduce the concentration ofthe mixed liquid), the temperature increase can be greater.

Therefore, it is possible to adjust conditions to perform optimalpeeling by appropriately selecting the concentrations of the liquids tobe mixed, the mixing ratio, the amount and reactivity of the oxidizingsubstances, the temperatures of the solutions prior to mixing, etc.

Although the case is described above where the highly concentratedinorganic acid solution is mixed with the oxidizing solution which alsois a low-concentration inorganic acid solution, the case will now bedescribed where the highly concentrated inorganic acid solution and theoxidizing solution are supplied sequentially.

Table 1 illustrates a comparison of the times to peel a resist in thecase where a test piece having the resist formed on the surface thereofis immersed in a highly concentrated inorganic acid solution andsubsequently immersed in an oxidizing solution. The highly concentratedinorganic acid solution was a concentrated sulfuric acid solution havinga sulfuric acid concentration of 98 weight percent. The oxidizingsolution was a dilute sulfuric acid solution having a sulfuric acidconcentration of 70 weight percent produced by electrolysis. Thetemperature of each of the highly concentrated inorganic acid solutionand the oxidizing solution was, as an example, about 100 to 110° C.

TABLE 1 IMMERSION TIME TIME TO PEELING SAMPLE IN CONCENTRATED AFTERIMMERSING IN NO. SULFURIC ACID OXIDIZING SOLUTION 1 0 sec 120 sec  2 10sec  20 sec 3 5 sec 15 sec 4 1 sec 15 sec

As illustrated in table 1, in the case where immersion in the highlyconcentrated inorganic acid solution (the concentrated sulfuric acidsolution having a sulfuric acid concentration of 98 weight percent) wasnot performed (the case of Sample No. 1), it took 120 seconds for theresist to peel. Conversely, it was shown that in the cases where theimmersion in the highly concentrated inorganic acid solution (theconcentrated sulfuric acid solution having the sulfuric acidconcentration of 98 weight percent) was performed (the cases of SamplesNos. 2 to 4), it took only about 20 seconds for the resist to peel; andthe processing time (the peeling time) was shortened drastically.Moreover, it was shown that even in the case where the time of theimmersion in the highly concentrated inorganic acid solution (theconcentrated sulfuric acid solution having the sulfuric acidconcentration of 98 weight percent) was short, the time for the resistto peel was not affected greatly.

FIG. 5 is a graph illustrating the relationship between the peeling timeand the number of times being supplied sequentially. The sample numbersare plotted on the vertical axis. The time for a resist formed on thetest piece surface to peel (the peeling time) is plotted on thehorizontal axis. D1 of FIG. 5 illustrates the case of immersion in aconcentrated sulfuric acid solution having a sulfuric acid concentrationof 98 weight percent; and D2 illustrates the case of immersing in anoxidizing solution produced by electrolyzing a dilute sulfuric acidsolution having a sulfuric acid concentration of 70 weight percent. Thetemperature of each of the concentrated sulfuric acid solution havingthe sulfuric acid concentration of 98 weight percent and the oxidizingsolution was, as an example, about 100 to 110° C.

Sample No. 10 is the case of immersion once in the concentrated sulfuricacid solution having the sulfuric acid concentration of 98 weightpercent for 1 second (the D1 portion). It was shown that in this case,it took about 16 seconds for the resist to peel.

Sample No. 11 is the case where the immersion in the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent for 1 second (the D1 portion) and an immersion in theoxidizing solution for 4 seconds (the D2 portion) were performedsequentially. In this case, the resist had peeled when the immersion inthe concentrated sulfuric acid solution having the sulfuric acidconcentration of 98 weight percent was performed twice and the immersionin the oxidizing solution was performed twice. It was shown that thetime for the resist to peel was 10 seconds, and the processing time wasshortened.

Sample No. 12 is the case where the immersion in the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent for 1 second (the D1 portion) and the immersion in theoxidizing solution for 1 second (the D2 portion) were performedsequentially. In this case, the resist had peeled when the immersion inthe 98 weight percent concentrated sulfuric acid solution was performedfour times and the immersion in the oxidizing solution was performedfour times. It was shown that the time for the resist to peel was 8seconds, and the processing time was shortened even more.

Thus, the processing time can be shortened by increasing the number ofimmersions and repeating sequentially. As illustrated in table 1, evenin the case where the immersion time in the concentrated sulfuric acidsolution was short, the time for the resist to peel was not affectedgreatly. Therefore, the processing time can be shortened by repeatedlyperforming immersions for somewhat short times.

FIG. 6 is a graph illustrating effects of the processing temperature(the solution temperature). The sample numbers are plotted on thevertical axis. The time for a resist formed on the test piece surface topeel (the peeling time) is plotted on the horizontal axis. E1 of FIG. 6illustrates the case of immersion in a concentrated sulfuric acidsolution having a sulfuric acid concentration of 98 weight percent; andE2 illustrates the case of immersion in an oxidizing solution producedby electrolyzing a dilute sulfuric acid solution having a sulfuric acidconcentration of 70 weight percent.

Sample No. 20 is the case where the temperature of the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent was room temperature and the temperature of the oxidizingsolution was 75° C.; and the resist was peeled by immersing in theconcentrated sulfuric acid solution having the sulfuric acidconcentration of 98 weight percent for 5 seconds and then immersing inthe oxidizing solution. In this case, the time for the resist to peelwas 520 seconds.

Sample No. 21 is the case where the temperature of the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent was 75° C.; the temperature of the oxidizing solution was75° C.; and the resist was peeled by immersing in the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent for 5 seconds and then immersing in the oxidizingsolution. In this case, the time for the resist to peel was 360 seconds.

Sample No. 22 is the case where the temperature of the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent was 100° C.; the temperature of the oxidizing solutionwas 75° C.; and the resist was peeled by immersing in the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent for 5 seconds and then immersing in the oxidizingsolution. In this case, the time for the resist to peel was 80 seconds.

Sample No. 23 is the case where the temperature of the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent was 100° C.; the temperature of the oxidizing solutionwas 100° C.; and the resist was peeled by immersing in the concentratedsulfuric acid solution having the sulfuric acid concentration of 98weight percent for 5 seconds and then immersing in the oxidizingsolution. In this case, the time for the resist to peel was 20 seconds.

Thus, although the processing time shortens as the processingtemperature (the solution temperature) is increased, increasing thetemperature too high may cause problems regarding the allowabletemperature and strength of the components of the cleaning system (e.g.,the piping lines, open/shut valves, pumps, and tanks of each unit, thecleaning processing unit cover, etc.). The components often are formedof, for example, fluorocarbon resin, etc., to increase the chemicalresistance of the portions in contact with the highly concentratedinorganic acid solution and the oxidizing solution. In such a case, thenecessary strength may not be possible in the case where the temperatureis too high.

Therefore, considering shortening the processing time and the allowabletemperature, strength, etc., of the cleaning system, it is favorable forthe temperatures of the highly concentrated inorganic acid solution andthe oxidizing solution to be not less than 100° C. and not more than110° C. In such a case, the processing temperature (the solutiontemperature) can be increased even more while reducing the thermal loadon the cleaning system by utilizing the heat of reaction describedabove. In the case where the heat of reaction is utilized, theprocessing temperature (the solution temperature) can be not less than100° C. and not more than 150° C.

A cleaning method according to this embodiment will now be described.

FIG. 7 is a flowchart illustrating the cleaning method.

First, an oxidizing solution including oxidizing substances (e.g.,peroxomonosulfuric acid and peroxodisulfuric acid) is produced byelectrolyzing a dilute sulfuric acid solution (step S1-1). In such acase, the oxidizing substances can be produced efficiently by making thesulfuric acid concentration of the dilute sulfuric acid solution notless than 30 weight percent and not more than 70 weight percent.

Then, the temperature of the produced oxidizing solution is adjusted(step S1-2). Although such a temperature adjustment is not alwaysnecessary, it is favorable for the temperatures of the solutions to beadjusted to be not less than 100° C. and not more than 110° C. asdescribed above. The temperature adjustment can be performed on any ofthe produced oxidizing solution, the oxidizing solution duringproduction (during the electrolysis), and the dilute sulfuric acidsolution supplied for the electrolysis.

The temperature of the highly concentrated inorganic acid solution isadjusted (step S2). Examples of a highly concentrated inorganic acidsolution include, for example, an inorganic acid solution having aninorganic acid concentration not less than 90 weight percent. Forexample, a concentrated sulfuric acid solution having a sulfuric acidconcentration not less than 90 weight percent, etc., may be used.Although such a temperature adjustment is not always necessary, it isfavorable for the temperatures to be adjusted to be not less than 100°C. and not more than 110° C. as described above.

Then, the highly concentrated inorganic acid solution is suppliedindividually, sequentially, or substantially simultaneously with theoxidizing solution to the surface of the object W to be cleaned (stepS3). The supplying may be performed from a dispense unit and the likefor each of the objects W to be cleaned and by sequentially immersing inthe highly concentrated inorganic acid solution and the oxidizingsolution. Also, for example, the supplying may be performedindividually, sequentially, or substantially simultaneously fromseparate piping systems for the highly concentrated inorganic acidsolution and the oxidizing solution. So-called single wafer processing,batch processing, and the like may be used.

The processing time (the peeling time) can be shortened even more byrepeatedly performing the processing of supplying the highlyconcentrated inorganic acid solution (e.g., the concentrated sulfuricacid solution) and the processing of supplying the oxidizing solutionincluding the oxidizing substances (e.g., electrolyzed sulfuric acidproduced by electrolyzing dilute sulfuric acid) a prescribed number oftimes to the surface of the object W to be cleaned.

In such a case, it is unnecessary to provide a process to supply arinsing fluid to the surface of the object W to be cleaned between thesupplying of the highly concentrated inorganic acid solution and thesupplying of the oxidizing solution. Therefore, the manufacturingprocesses can be simplified and the processing time (the peeling time)can be shortened.

FIG. 8 is a flowchart illustrating a cleaning method according toanother embodiment.

In this embodiment, the oxidizing solution and the highly concentratedinorganic acid solution are mixed; and the mixture is supplied to thesurface of the object W to be cleaned.

First, an oxidizing solution including oxidizing substances (e.g.,peroxomonosulfuric acid and peroxodisulfuric acid) is produced byelectrolyzing a dilute sulfuric acid solution (step S10). In such acase, the oxidizing substances can be produced efficiently by making thesulfuric acid concentration of the dilute sulfuric acid not less than 30weight percent and not more than 70 weight percent.

Then, the oxidizing solution and the highly concentrated inorganic acidsolution are mixed to produce a cleaning liquid (step S11). At thistime, the inorganic acid concentration and the amount of the oxidizingsubstances in the cleaning liquid are appropriately adjusted. Examplesof the highly concentrated inorganic acid solution include an inorganicacid solution having, for example, an inorganic acid concentration notless than 90 weight percent. For example, a concentrated sulfuric acidsolution having a sulfuric acid concentration not less than 90 weightpercent, etc., may be used.

Continuing, the temperature of the produced cleaning liquid is adjusted(step S12). Although such a temperature adjustment is not alwaysnecessary, it is favorable for the temperature of the cleaning liquid tobe adjusted to be not less than 100° C. and not more than 110° C. asdescribed above. The temperature adjustment can be performed on theoxidizing solution and the highly concentrated inorganic acid solutionprior to mixing.

Then, the cleaning liquid (the mixed liquid of the highly concentratedinorganic acid solution and the oxidizing solution) is supplied to thesurface of the object W to be cleaned (step S13). The supplying may beperformed from a dispense unit and the like for each of the objects W tobe cleaned and by immersing in the cleaning liquid. So-called singlewafer processing, batch processing, and the like may be used.

In this embodiment as illustrated in FIG. 7 and FIG. 8, dilute sulfuricacid solution is electrolyzed. Therefore, the electrolysis efficiency ishigh and more oxidizing substances can be produced efficiently. In sucha case, the highly concentrated inorganic acid solution and theoxidizing solution are mixed after the oxidizing substances are produced(after the electrolysis). Therefore, the electrolysis efficiency is notaffected.

Also, processing using a cleaning liquid having a high concentration ofinorganic acid is possible by using the highly concentrated inorganicacid solution, or processing on the surface of the object W to becleaned is possible with a high-concentration inorganic acid.

Therefore, the processing time (the peeling time) can be shorteneddrastically because processing (cleaning) can be performed with a highconcentration of an inorganic acid such as sulfuric acid and a largeamount of oxidizing substances.

While a high-speed operation semiconductor device is manufactured byimplanting an impurity with a high dose, an altered layer is formed inthe surface of the resist by the implanting of the impurity with thehigh dose. The resist having such an altered layer does not peel easily;and the desired peeling margin unfortunately cannot be obtained.

According to this embodiment, a solution including a highly concentratedinorganic acid and a large amount of oxidizing substances can besupplied to the surface of the object W to be cleaned. Therefore, thepeelability of a resist can be increased even in the case where analtered layer is formed in the resist.

A heat of reaction can be generated by mixing the highly concentratedinorganic acid solution with an oxidizing solution, which also is alow-concentration inorganic acid solution, prior to supplying to theobject W to be cleaned or on the object W to be cleaned. Therefore, thetemperature increase of the components of the cleaning system can besuppressed; and the reactivity of the oxidizing substances can beincreased by increasing the temperature of the mixed liquid. As aresult, the processing time (the peeling time) can be shortened evenmore.

A method for manufacturing a microstructure according to this embodimentwill now be described.

Examples of a method for manufacturing a microstructure include, forexample, a method for manufacturing a semiconductor device. Here, themanufacturing processes of the semiconductor device include theso-called front-end processes such as the processes that form a patternon a substrate (wafer) surface by film formation, resist coating,exposing, developing, etching, resist removal, etc., the inspectionprocesses, cleaning processes, heat treatment processes, impurityintroduction processes, diffusion processes, planarizing processes, etc.The so-called back-end processes include the assembly processes ofdicing, mounting, bonding, encapsulation, etc., the functional andreliability inspection processes, etc.

In such a case, the resist removal (peeling) can be performed rapidly byusing, for example, the cleaning method and the cleaning systemdescribed above in the resist removal process. Known technology may beapplied for the processes other than those of the cleaning method andthe cleaning system according to this embodiment described above, andtherefore a detailed description thereof is omitted.

Although a method for manufacturing a semiconductor device isillustrated as one example of the method for manufacturing themicrostructure, the method for manufacturing the microstructure is notlimited thereto. For example, applications are possible in fields suchas liquid crystal display devices, phase shift masks, micromachines inMEMS fields, precision optical components, etc.

In the cleaning system described above, it is not always necessary toprovide a configuration to circulate the solution. As illustrated inFIG. 9, the solution used in the cleaning processing unit 12 may berecovered by the returning tank 63 with contaminants and the like andthen subsequently discharged outside the system via the discharge pipingline 75.

Such processing may be used not only to remove a resist made of anorganic substance, but also to similarly remove metal impurities,particles, and dry etching residue.

A robot may be provided to transfer the objects to be cleaned. Each ofthe tank 60 retaining the dilute sulfuric acid solution and the tank 51retaining the highly concentrated inorganic acid solution may beconnected to a line of a factory to automatically replenish thesolution. A rinse bath may be provided for rinsing of the object to becleaned after removing the contaminants. Such a rinse bath may includean overflow control device and a temperature control device using anin-line heater. It is suitable to use quartz as the material quality ofthe rinse bath.

However, it is unnecessary to provide a process to supply a rinsingfluid to the surface of the object to be cleaned between the supplyingof the highly concentrated inorganic acid solution (e.g., theconcentrated sulfuric acid solution) and the supplying of the oxidizingsolution (e.g., the electrolyzed sulfuric acid produced by electrolyzingdilute sulfuric acid). It is sufficient to repeatedly perform theprocessing of supplying the highly concentrated inorganic acid solution(e.g., the concentrated sulfuric acid solution) to the object W to becleaned and the processing of supplying the oxidizing solution includingthe oxidizing substances (e.g., the electrolyzed sulfuric acid producedby electrolyzing dilute sulfuric acid) to the object W to be cleaned aprescribed number of times. Therefore, the manufacturing processes canbe simplified and the processing time (the peeling time) can beshortened.

Hereinabove, embodiments are illustrated. However, the invention is notlimited to the descriptions thereof.

Design modifications appropriately made by one skilled in the art inregard to the embodiments described above also are included in the scopeof the invention to the extent that features of the invention areincluded.

For example, the configurations, dimensions, material qualities,dispositions, etc., of the components of the cleaning systems describedabove are not limited to those illustrated herein and may beappropriately modified.

Further, the components of the embodiments described above may becombined within the extent of feasibility; and such combinations alsoare included in the scope of the invention to the extent that thefeatures of the invention are included.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modification as would fall within thescope and spirit of the inventions.

1. A cleaning method, comprising producing an oxidizing solutionincluding an oxidizing substance by electrolyzing a dilute sulfuric acidsolution, and supplying a highly concentrated inorganic acid solutionindividually, sequentially, or substantially simultaneously with theoxidizing solution to a surface of an object to be cleaned.
 2. Themethod according to claim 1, wherein the supplying of the highlyconcentrated inorganic acid solution to the surface of the object to becleaned and the supplying of the oxidizing solution to the surface ofthe object to be cleaned are performed repeatedly.
 3. The methodaccording to claim 1, wherein a sulfuric acid concentration of thedilute sulfuric acid solution is not less than 30 weight percent and notmore than 70 weight percent.
 4. The method according to claim 1, whereinthe highly concentrated inorganic acid solution is a concentratedsulfuric acid solution having a sulfuric acid concentration not lessthan 90 weight percent.
 5. The method according to claim 1, wherein theoxidizing substance includes at least one selected fromperoxomonosulfuric acid and peroxodisulfuric acid.
 6. The methodaccording to claim 1, wherein at least one selected from a temperatureof the oxidizing solution and a temperature of the highly concentratedinorganic acid solution is not less than 100° C. and not more than 110°C.
 7. The method according to claim 1, wherein a heat of reaction whenthe highly concentrated inorganic acid solution and the oxidizingsolution are mixed on the surface of the object to be cleaned isutilized to perform a temperature adjustment of a solution.
 8. Themethod according to claim 1, wherein a supplying of a rinsing fluid tothe surface of the object to be cleaned is not performed between thesupplying of the highly concentrated inorganic acid solution and thesupplying of the oxidizing solution.
 9. The method according to claim 1,wherein a resist is formed on the surface of the object to be cleaned, asurface of the resist having an altered layer.
 10. A cleaning system,comprising: a sulfuric acid electrolysis unit including an anode, acathode, a partitioning membrane provided between the anode and thecathode, an anode chamber provided between the anode and thepartitioning membrane, and a cathode chamber provided between the anodeand the partitioning membrane, the sulfuric acid electrolysis unitproducing an oxidizing substance in the anode chamber by electrolyzing adilute sulfuric acid solution; a dilute sulfuric acid supply unitsupplying a dilute sulfuric acid solution to the anode chamber and thecathode chamber; a cleaning processing unit performing a cleaningprocessing of an object to be cleaned; an inorganic acid supply unitsupplying a highly concentrated inorganic acid solution to the cleaningprocessing unit; and an oxidizing solution supply unit supplying anoxidizing solution including the oxidizing substance to the cleaningprocessing unit, the highly concentrated inorganic acid solution beingsupplied to the cleaning processing unit by the inorganic acid supplyunit individually, sequentially, or substantially simultaneously withthe oxidizing solution supplied by the oxidizing solution supply unit.11. The system according to claim 10, further comprising a solutioncirculation unit that recovers at least one selected from the highlyconcentrated inorganic acid solution and the oxidizing solutiondischarged from the cleaning processing unit and resupplies the at leastone to the cleaning processing unit.
 12. The system according to claim11, wherein the solution circulation unit recovers at least one selectedfrom the highly concentrated inorganic acid solution and the oxidizingsolution discharged from the cleaning processing unit and resupplies theat least one to the cleaning processing unit via the sulfuric acidelectrolysis unit.
 13. The system according to claim 12, wherein thesulfuric acid electrolysis unit produces an oxidizing substance in theanode chamber by electrolyzing a dilute sulfuric acid solution and atleast one selected from the highly concentrated inorganic acid solutionand the oxidizing solution, the dilute sulfuric acid solution beingsupplied by the dilute sulfuric acid supply unit, the at least one beingsupplied by the solution circulation unit.
 14. The system according toclaim 10, wherein a sulfuric acid concentration of the dilute sulfuricacid solution is not less than 30 weight percent and not more than 70weight percent.
 15. The system according to claim 10, wherein the highlyconcentrated inorganic acid solution is a concentrated sulfuric acidsolution having a sulfuric acid concentration not less than 90 weightpercent.
 16. The system according to claim 10, wherein the inorganicacid supply unit includes a heater performing a temperature control ofthe inorganic acid solution.
 17. The system according to claim 11,wherein the solution circulation unit includes a heater performing atemperature control of the oxidizing solution.
 18. The system accordingto claim 11, wherein a heater is provided in at least one selected frompiping supplying the oxidizing solution to the cleaning processing unitand piping supplying the highly concentrated inorganic acid solution tothe cleaning processing unit.
 19. The system according to claim 11,wherein at least one selected from the anode and the cathode includes aconductive diamond film formed on a surface of a conductive base member.20. A method for manufacturing a microstructure comprising cleaning anobject to be cleaned by the cleaning method according to claim 1 andforming a microstructure.